This invention relates generally to an adjustment circuit for voltage division, particularly to an adjustment circuit applicable to a voltage divider with constant current for adjusting divided resistance or resolution in a respectively larger scope while keeping the total resistance unchanged.
A voltage divider is implemented frequently in circuits to divide voltage for output of an expected voltage value. For convenience, an adjustable voltage divider is preferred for trimming in the case an offset to some extent is found in the value of the expected output voltage.
In a conventional adjustment method shown in FIG. 1, a serial resistor Rn(n=0, 1, 2 . . . N) is connected in series and paired in parallel with a corresponding switch S0, S1 . . . SN apiece to form an adjustable voltage-dividing resistor xcex94R, and an output voltage Vo equal to Vdd(Rout+xcex94Rxe2x80x2)/(Rin+Rout+xcex94R) is obtained (where xcex94Rxe2x80x2 is a valid portion of voltage-dividing resistor equal to 0 or xcex94R). Examples are presented as in the following:
If the switches SA and SB are turned xe2x80x9cONxe2x80x9d while the rest switches don""t care, then
Vo=Vddxc3x97Rout÷(Rin+Rout).
If the switch SA is turned xe2x80x9cONxe2x80x9d only while the rest switches are turned xe2x80x9cOFFxe2x80x9d; then
Vo=Vddxc3x97(Rout+R0+R1+R2+R3+ . . . +Rn)/(Rin+Rout+R0+R1+R2+R3+ . . . +Rn).
If the switches SA and S0 are turned xe2x80x9cONxe2x80x9d while the rest switches are turned xe2x80x9cOFFxe2x80x9d; then
Vo=Vddxc3x97(Rout+R1+R2+R3+ . . . +Rn)/(Rin+Rout+R1+R2+R3+ . . . +Rn).
If the switches SA, S0, and S1 are turned xe2x80x9cONxe2x80x9d while the rest switches are turned xe2x80x9cOFFxe2x80x9d; then
Vo=Vddxc3x97(Rout+R2+R3+R4+ . . . +Rn)/(Rin+Rout+R2+R3+R4+ . . . +Rn).
If the switch SB is turned xe2x80x9cONxe2x80x9d only while the rest switches are turned xe2x80x9cOFFxe2x80x9d; then
Vo=Vddxc3x97Rout/(Rin+Rout+R0+R1+R2+R3+ . . . +Rn).
If the switch SB and S0 are turned xe2x80x9cONxe2x80x9d while the rest switches are turned xe2x80x9cOFFxe2x80x9d; then
Vo=Vddxc3x97Rout/(Rin+Rout+R1+R2+R3+ . . . +Rn).
If the switches SB, S0, and S1 are turned xe2x80x9cONxe2x80x9d while the rest switches are turned xe2x80x9cOFFxe2x80x9d; then
Vo=Vddxc3x97Rout/(Rin+Rout+R2+R3+R4+ . . . +Rn).
The switches are properly controlled such that the adjustable voltage-dividing resistor xcex94R can be adjusted proportionally to obtain a desired output voltage Vo. Now, suppose Rn=2nR, then xcex94R=(S020+S121+ . . . +Sn2n)R, where Sn is 0 or 1. When Sn in FIG. 1 is turned xe2x80x9cONxe2x80x9d, Sn is 0, otherwise, Sn is 1 and R=1 accordingly, so that xcex94R is adjustable proportionally in the range of (S020+S121+ . . . +Sn2n) as mentioned. However, such a voltage divider structure is inapplicable to a voltage division system that requires a constant current because of its variable resultant resistance and current, and is defective in adjusting or providing multiple outputs Vo.
For improvement, an amended design has been proposed later on as shown in FIG. 2, wherein an adjustable voltage-dividing resistor xcex94R comprises a serial resistor Rn including resistor R0, R1, R2, . . . Rn connected in series and corresponding switch S0, S1, . . . Sn in parallel to obtain an output voltage V01=Vddxc3x97(Rout 1+Rout 2+xcex94R1xe2x80x2+xcex94R2)/(Rin+Rout 1+Rout 2+xcex94R1+xcex94R2), where xcex94R1xe2x80x2 is a variable and another output voltage V02=Vddxc3x97(Rout 2+xcex94R2xe2x80x2)/(Rin+Rout 1+Rout 2+xcex94R1+xcex94R2), where xcex94R2xe2x80x2 is a variable.
Taking V01 for example, adjustment may be made as the following:
If the switch S0 is turned xe2x80x9cONxe2x80x9d while the rest switches are turned xe2x80x9cOFFxe2x80x9d, then
V01=Vddxc3x97(Rout 1+Rout 2+R0+R1+ . . . +Rn+xcex94R2)/(Rin+Rout 1+Rout 2+R0+R1+ . . . +Rn+xcex94R2).
If the switch S1 is turned xe2x80x9cONxe2x80x9d while the rest switches are turned xe2x80x9cOFFxe2x80x9d, then
V01=Vddxc3x97(Rout 1+Rout 2+R1+ . . . +Rn+xcex94R2)/(Rin+Rout 1+Rout 2+R0+R1+ . . . +Rn+xcex94R2).
The variable valid voltage-dividing resistor xcex94R1xe2x80x2 can be adjusted to obtain a desired or multiple outputs Vo by controlling the switches properly in a voltage division system operated under a constant current, whereas, the voltage-dividing resistor xcex94R is not suited to be adjusted proportionally in the range of (S020+S121+ . . . +Sn2n).
The primary object of this invention is to provide an adjustment circuit for voltage division, which is implemented in an adjustable voltage-dividing resistor xcex94R comprising a symmetrically mapped serial resistor(Rn) and paired switches(Sn), wherein a valid portion of voltage-dividing resistor xcex94Rxe2x80x2 can be adjusted proportionally in the range of (S0R0+S1R1+ . . . +SnRn).
For more detailed information regarding advantages or features of this invention, at least an example of preferred embodiment will be elucidated below with reference to the annexed drawings.